Genetically predisposed individuals, who make up about 10% of the population, become hypersensitized (allergic) to antigens from a variety of environmental sources to which they are exposed. Those antigens that can induce immediate and/or delayed types of hypersensitivity are known as allergens. (King, T. P., Adv. Immunl. 23:77-105, (1976)). Anaphylaxis or atopy, which includes the symptoms of hay fever, asthma, and hives, is one form of immediate allergy. It can be caused by a variety of atopic allergens, such as products of grasses, trees, weeds, animal dander, insects, food, drugs, and chemicals.
The antibodies involved in atopic allergy belong primarily to the IgE class of immunoglobulins. IgE binds to mast cells and basophils. Upon combination of a specific allergen with IgE bound to mast cells or basophils, the IgE may be cross-linked on the cell surface, resulting in the physiological effects of IgE-antigen interaction. These physiological effects include the release of, among other substances, histamine, serotonin, heparin, a chemotactic factor for eosinophilic leukocytes and/or the leukotrienes, C4, D4, and E4, which cause prolonged constriction of bronchial smooth muscle cells (Hood, L. E. et al. Immunology (2nd ed.), The Benjamin/Cumming Publishing Co., Inc. (1984). These released substances are the mediators which result in allergic symptoms caused by a combination of IgE with a specific allergen. Through them, the effects of an allergen are manifested. Such effects may be systemic or local in nature, depending on the route by which the antigen entered the body and the pattern of deposition of IgE on mast cells or basophils. Local manifestations generally occur on epithelial surfaces in the location at which the allergen entered the body. Systemic effects can include anaphylaxis (anaphylactic shock), which is the result of an IgE-basophil response to circulating (intravascular) antigen.
The sub-tropical grass Sorghum halepense (Johnson grass) is representative of a genus which is widely cultivated as a cereal grain plant. Sorghums are the major cereal grain cropped in Africa and are also cultivated in the U.S., India, Pakistan and northern China. Johnson grass is heat resistant and well adapted to warm conditions. The pollen of Johnson grass, Bahia and Bermuda grass constitute the allergenically important grass pollens in the southern United States (French and Major, J. Allergy 1:286-291 (1930); Martin et al., Ann. Allergy 54:992-104 (1985)). Both Johnson grass and Bahia are members of the subfamily Panicoideae, which also includes the economically important genera Saccharum (sugar cane) and Zea (maize) (Watson, 1990, Reproductivity Versatility in the Grasses (G. P. Chapman ed.) Cambridge University Press, pp. 258-265)).
The allergenic importance of Johnson grass in areas where it has wide distribution has been reported in the literature (French and Major, 1930, supra). It appears to share allergenicity with both Bermuda grass from subfamily Chlorideae, and the temperate grasses of subfamily Pooideae (Martin et al., 1985, supra). The Group I allergen of Johnson grass has been shown to have antigenic cross-reactivity with other Group I allergens (Singh and Knox, Int. Arch. Alll. Appl. Immunol. 72:243-248 (1985)).
Treatment of sensitivity to grass pollen allergens by administration of pollen extract to effect hyposensitization to the allergen has been attempted. Hyposensitization using pollen extract, however, has drawbacks in that it can elicit anaphylaxis if high doses are used, whereas when low doses are used to avoid anaphylaxis, treatment must be continued for several years to build up a tolerance for the extract. Despite the attention grass pollen allergens have received, definition or characterization of the Johnson grass pollen allergens responsible for its adverse effects on people is far from complete.